Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 DOI 10.1186/s12906-016-1405-5 RESEARCH ARTICLE Open Access Sex differences in acupuncture effectiveness in animal models of Parkinson's disease: a systematic review Sook-Hyun Lee1, Maurits van den Noort2, Peggy Bosch3 and Sabina Lim1,2,4* Abstract Background: Many animal experimental studies have been performed to investigate the efficacy of acupuncture in Parkinson’s disease (PD) Sex differences are a major issue in all diseases including PD However, to our knowledge, there have been no reviews investigating sex differences on the effectiveness of acupuncture treatment for animal PD models The current study aimed to summarize and analyze past studies in order to evaluate these possible differences Method: Each of databases (MEDLINE, EMBASE, the Cochrane Library, Korean medical databases, and the China National Knowledge Infrastructure) was searched from its inception through March 2015 without language restrictions Results: We included studies of the use of acupuncture treatment in animal models of PD A total of 810 potentially relevant articles were identified, 57 of which met our inclusion criteria C57/BL6 mice were used most frequently (42 %) in animal PD models Most of the studies were carried out using only male animals (67 %); only study (2 %) was performed using solely females The further 31 % of the studies used a male/female mix or did not specify the sex Conclusions: The results of our review suggest that acupuncture is an effective treatment for animal PD models, but there is insufficient evidence to determine whether sex differences exist Future studies of acupuncture treatment for PD should use female animal models because they reflect the physiological characteristics of both males and females to fully evaluate the effect and the safety of the treatment for each sex Keywords: Electro-acupuncture, Manual acupuncture, Bee-venom acupuncture, C57/BL6, Acupuncture point Background Parkinson’s disease (PD) is a progressive neurodegenerative disease caused by the loss of dopaminergic neurons in the substantia nigra [1] PD usually occurs in individuals over 50 years of age, and its incidence and prevalence increases among individuals approximately 60 years of age and older PD has become more common due to the rapid aging of human populations around the world [2] Epidemiological studies have * Correspondence: lims@khu.ac.kr Department of Applied Korean Medicine, Graduate School, Kyung Hee University, Seoul, Republic of Korea Research Group of Pain and Neuroscience, WHO Collaborating Center for Traditional Medicine, East–west Medical Research Institute, Kyung Hee University, Seoul, Republic of Korea Full list of author information is available at the end of the article reported that the incidence of PD is 1.5–2 times higher in men than in women, and the onset of symptoms may occur later in women due to the neuroprotective effects of estrogen [3] For the disease manifestations of PD, women have higher Unified Parkinson’s Disease Rating Scale (UPDRS) motor scores, but present with dyskinesia, tremor, and PD-related complications more often than men [4] Because the FDA reported that eight out of ten new drugs that had been sold on the market were discontinued because they resulted in far more detrimental side effects in women, the sex perspective began to be discussed in many other fields as well [5] Adverse drug reactions can be caused by the physiological difference between men and women, and women can be © The Author(s) 2016 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 more vulnerable to a particular drug [6] Because sex is often not considered an important variable in animal research with the exception of research related to features of a particular sex, such as reproduction and endocrine secretion, the overwhelming majority of experimental research uses only males and many studies not even disclose the sex of the experimental animals Basic research studies using cells in culture also often fail to present the sex of the organism from which the cell strain originated, but the results of such basic research has been applied generally to humans Because medical research studies are performed primarily by male researchers [7–9], the research subjects are also mostly males [10–12], and there has been a tendency to be careless of females [13], which can aggravate treatment problems related to the physiological differences between men and women The National Institutes of Health (NIH) requires applicants to report their cell and animal inclusion plans as part of the preclinical experimental design [14] Therefore, studies are being performed to determine what sex differences need to be accounted for in preclinical and clinical stages, and the importance of the applying these principles is being highlighted [15] PD treatment options include pharmacological treatment, non-pharmacological treatment, surgical therapy, and dopaminergic cell transplantation [15] Acupuncture has long been employed for numerous disorders, and it has been traditionally used to relieve PD-related symptoms and to delay the clinical progression of PD symptoms [16] We have reported that acupuncture exerts increased neuroprotective effects in regions including the substantia nigra, caudate, thalamus, and putamen in animal models of PD [17–20] Acupuncture was also found to inhibit microglial activation, inflammation, and iron-related oxidative damage in PD [21] Sex differences have emerged recently as an important issue, but sufficient efficacy tests for sex differences in acupuncture, as in preclinical studies for drug development, have not yet been performed It is necessary to clarify efficacy differences according to sex in order to more effectively utilize acupuncture in clinical practice Therefore, we carried out the present study to identify whether adequate research has been conducted so far to determine the sex differences in the efficacy of acupuncture Specifically, we analyzed past studies of acupuncture treatment conducted in animal PD models, and determined whether the body of data was sufficient to determine the effects of sex differences on the effectiveness of acupuncture treatment This review provides the basis for establishing whether future animal model studies are necessary to determine possible sex-related differences in the efficacy of acupuncture for PD Page of 10 Methods Search methods for the identification of studies The search was performed without restrictions on language or year of publication We searched Medline, EMBASE, and the Cochrane Central Register of Controlled Trials from the inception of each database through March 2015 For Korean publications, we searched three Korean medical databases (Research Information Service System, National Discovery for Science Leaders, and OASIS) For Chinese articles, we searched the China National Knowledge Infrastructure The keywords used for the search were the following: “Parkinson’s disease” OR “Parkinson” AND “acupuncture” OR “acupoints” OR “electroacupuncture” OR “electro-acupuncture” OR “auriculotherapy” OR “auriculoacupuncture” OR “bee venom acupuncture” in each database language The search strategy was adjusted for each database Inclusion/exclusion criteria We included studies of the use of acupuncture treatment in animal PD models Trials were excluded if the study designs did not evaluate the effectiveness of acupuncture in animal PD models, or if they reported insufficient data No search restrictions on language or publication forms were imposed During the first stage of selection/ exclusion, titles and abstracts were analyzed, and literature that had no relevance to our study was excluded The second stage of selection/exclusion involved analyzing the full text of particular studies, because it was impossible to determine the relevance of the studies based solely on the abstracts Data extraction Two reviewers (LSH and KJY) independently reviewed the data extracted from each article using a standardized data extraction form and reached consensus on all items The extracted data included the type of animal PD models, the sex of the animal PD models, the methods used to induce PD, the types of acupuncture, the acupuncture points, and the effectiveness of the treatment Results Study description We identified 810 publications, 57 of which met the eligibility criteria (Fig 1) The 57 articles were published from 1996 to 2014 The characteristics of the studies are summarized in Table [7–12, 18, 19, 21–69] Animals of PD models The animals of PD models included mice (C57/BL6 and ICR) and rats (Sprague–Dawley, and Wistar) (Fig 2) The most frequently used animal PD model was C57/ BL6, which was used in 24 articles, followed by SD and Wistar, each of which were used in 15 articles, and ICR Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 Page of 10 Fig Flowchart of the study selection process and undefined animals, which were used in one article each All of the studies using C57/BL6 animals used only males Of the studies using SD animals, ten used males only, four used a male/female mix, and one used animals with undefined sex Of the studies using Wistar animals, nine used a male/female mix, two used males only, three used animals with undefined sex, and one study used females only Methods used to induce PD The drugs 6-hydroxydopamine (6-OHDA), 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP), and rotenone, as well as medial forebrain bundle (MFB) transection, were used to induce PD in the animal models (Fig 3) 6OHDA was used in 47 % (27) of the studies, MPTP was used in 44 % (25) of the studies, and rotenone was used in % (4) of the studies MFB transection was used in % (1) of the studies Of the studies using 6-OHDA, 13 used a male/female mix, nine used only males, and five used animals with undefined sex All of the studies using MPTP or Rotenone used only male animals The study using MFB transection used only females Therefore, three out of the four PD induction models studied were only used in animals of a single sex Only the results of 6-OHDA induced animal PD models could potentially be compared between the sexes Types of acupuncture Electro-acupuncture (EA) was used in 54 % (38) of the studies, manual acupuncture (MA) was used in 30 % (18) of the studies, and bee-venom (BV) acupuncture was used in 11 % (6) of the studies Of the studies using EA, 18 used only males, 11 used a male/female mix, three used animals of undefined sex, and one used only females Of the studies using MA, 14 used only males, two used a male/female mix, and two used animals with undefined sex All of the studies using BV acupuncture used only males (Fig 4) Acupuncture points Regardless of the type of acupuncture, the acupuncture points used consisted mainly of LR3, GB34, GV20, GV16, and ST36 (Additional file 1) LR3 was used in 35 % (20) of the studies, and GV34 and GV20 were each used in 26 % (16) of the studies Of the studies using LR3, 14 used only males, three used a male/female mix, and three used animals with undefined sex Of the studies using GB34, 14 used only males, and two used a male/female mix Of the studies using GV20, eight used only males, seven used a male/female mix, and one used animals with undefined sex Of the studies using GV16, seven used only males, three used a male/female mix, and three used animals with undefined sex Of the studies using ST36, four used only males, two used animals with undefined sex, and one used a male/female mix Behavioral test Behavioral analyses were carried out using the rotational behavior test, the pole-climbing test, the swimming test, and locomotor counts (Additional file 2) The rotational behavior test was used in 56 % (10) of the studies, the pole-climbing test was used in 22 % (6) of the studies, and the swimming test, and locomotor counts were each used in % (1) of the studies The rotational behavior First author (year) Type of animal PD models Sex of animal PD models Drugs used to induce PD Types of acupuncture Types of acupuncture points Evaluation of the treatment effectiveness Bai (2014a) [22] Undefined Undefined 6-OHDA EA GV20, EX-HN5 DA Bai (2014b) [8] Undefined Male 6-OHDA EA GV20, EX-HN5 Caspase-3 Feng (2014) [10] C57BL/6 Male MPTP MA Undefined Pole-climbing test, BDNF, TH, DA Yeo (2013) [19] C57BL/6 Male MPTP MA GB34, LR3 TH, gene expression Alvarez-Fischer (2013) [7] C57BL/6 Male MPTP BV Undefined DA, DOPAC, IL-1β, IL-6, TNF-α, HVA, TH, rotational test Ding (2013) [11] SD Male 6-OHDA EA LI4, LR3 nNOS, GFAP Wang (2013a) [9] SD Male Rotenone EA GV16, LR3 TH, COX-2 Wang (2013b) [23] SD Male Rotenone EA GV16, LR3 TH, p-p38 MARK, COX-2 Wang (2013c) [12] SD Male Rotenone EA GV16, LR3 TH, SOD, GSH, CAT, MDA Wang (2013d) [24] SD Male Rotenone EA GV16, LR3 UCH-L1, UBE1, Parkin, TH, α-synuclein Ding (2012) [25] SD Male 6-OHDA EA LI4, LR3 TH, GFAP, PCNA Huang (2012) [26] ICR Male MPTP EA GB34 Lamp 1, α-synuclein Lu (2012) [27] C57BL/6 Male MPTP EA GV20, GV16, GB34 Locomotor counts, swimming test, pole-climbing test Guo (2012) [28] SD Male 6-OHDA EA GV20, GV16, GB34 GSH, SOD, MDA, GSH-Px Yang (2011) [29] C57BL/6 Male MPTP EA PC7 Pole-climbing test, TH, DA, DOPAC, HVA Choi (2011) [18] C57/BL6 Male MPTP MA GB34, LR3 TH, DAT, gene expression Kim (2011) [30] C57BL/6 Male MPTP BV ST36 MAC-1, iNOS, TH Du (2011) [31] SD Male 6-OHDA EA GV20, GV14 GABA, rotational test C57BL/6 Male MPTP EA ST36, SP6 TH, DA, DOPAC, HVA, SOD, GSH, GSH-Px C57BL/6 Male MPTP BV GB34 TH Hong (2010) [34] C57BL/6 Male MPTP MA GB34 Gene expression Jun (2010) [35] C57BL/6 Male MPTP BV BL23 TH, caspase-3, iNOS Kim (2010) [36] C57BL/6 Male MPTP EA GB34, GB39 DA Park (2010) [37] C57BL/6 Male MPTP BV GB39, LI11, BL23 TH, MAC-1, HSP70 Sun (2010) [38] C57BL/6 Male MPTP MA GV20, GV14 Pole-climbing test, TH, DA, DOPAC Wang (2010a) [39] Wistar Undefined 6-OHDA EA GV16, LR3 TH, DA Wang (2010b) [40] Wistar Undefined 6-OHDA EA GV16, LR3,CV4, ST36 GDNF Wang (2010c) [41] C57/BL6 Male MPTP MA GV20, GV14 Pole-climbing test, TH, DA, NA, DOPAC, 5HIAA, 5HT Yu (2010) [42] Wistar Male 6-OHDA MA GB34, LR3, ST36, SP10 Rotational test, SOD, GSH-Px, CAT, GSH, MDA Huang (2010) [43] Wistar Male 6-OHDA EA LI4, LR3 Rotational test, BDNF, TrKB Page of 10 Wang (2011) [32] Doo (2010) [33] Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 Table Summary of acupuncture for animal PD models Choi (2009) [21] C57/BL6 Male MPTP MA LR3, GB34 TH, DAT Kim (2009) [44] C57BL/6 Male MPTP BV BL23 TH, MAC-1, HSP70 Wang (2009a) [45] Wistar Male, Female 6-OHDA EA GV20, EX-NH5 TH, BDNF Wang (2009b) [46] Wistar Male, Female 6-OHDA EA GV20, EX-NH5 TH, DAT Kim (2008) [47] C57BL/6 Male MPTP MA GB34 TH Guan (2008) [48] C57BL/6 Male MPTP EA GV20 Fn Wang (2008) [49] Wistar Male, Female 6-OHDA EA GV20, EX-NH5 TH Jeon (2008) [50] C57BL/6 Male MPTP EA GB34, SI3, BL62, ST36 Pole-climbing test, TH, DA, BDNF Xie (2007) [51] Wistar Undefined 6-OHDA MA GV20 Rotational test, MDA, NO, SOD Kang (2007) [52] C57BL/6 Male MPTP MA GB34, LR3 TH, COX-2, iNOS, DA, DOPAC, HVA Huang (2007) [53] SD Male 6-OHDA MA GB34, LR3 TH Luo (2007) [54] Wistar Male, Female 6-OHDA EA GV20, EX-NH5 NOS Wang (2007) [55] SD Male, Female 6-OHDA MA GV20, GV16, GB34 Rotational test, DA Jin (2006a) [56] Wistar Male, Female 6-OHDA EA Undefined GSH, GSH-Px,SOD, MDA, NOS Jin (2006b) [57] Wistar Male, Female 6-OHDA EA Undefined DA, HVA, DOPAC Ma (2006) [58] Wistar Male, Female 6-OHDA EA GV16, LR3 Rotational test, DA Tang (2006) [59] C57BL/6 Male MPTP EA LI4, LR3 BDNF Wang (2006) [60] SD Male, Female 6-OHDA EA GV16, LR6 Glutamic acid Kim (2006) [61] C57BL/6 Male MPTP MA LR8, LR4, LR2 TH Kim (2005) [62] SD Undefined 6-OHDA MA ST36 Rotational test, TH Ma (2005) [63] Wistar Male, Female 6-OHDA EA GV16, LR3 Rotational test, SOD, GSH, GSH-Px Wang (2005) [64] Wistar Undefined 6-OHDA MA GV16, LR3, CV4, ST36 TH Park (2003) [65] SD Male 6-OHDA MA GB34, LR3, LI4, LI11 Rotational test, TH, TrkB Liang (2002) [66] Wistar Female MFB transection EA GV14, GV21 TH, BDNF Lin (2000) [67] SD Male, Female 6-OHDA EA LR3, SP6, ST36, GB34 DA, HVA, DOPAC He (1998) [68] SD Male, Female 6-OHDA EA GV20, GV14 DA, NA, 5HT Zhu (1996) [69] C57BL/6 Male MPTP MA GV20 DA, DOPAC Page of 10 Abbreviations: BDNF Brain-derived neurotrophic factor, BV Bee-venom acupuncture, CAT Catalase, Caspase-3: caspase protein, COX-2 Cyclooxygenase-2, DA Dopamine, DAT Dopamine active transporter, DOPAC Dihydroxyphenyl acetic acid, EA Electro-acupuncture, Fn Ferritin, GABA gamma-aminobutyric acid, GDNF Glial cell-derived neurotrophic factor, GFAP Glial fibrillary acidic protein, GSH Glutathione, GSHpx Glutathione peroxidase, HSP70 70 kilo Dalton heat shock proteins, HVA Homovanillic acid, IL-1β Interleukin-1 beta, IL-6 Interleukin-6, iNOS Inducible nitric oxide synthase, Lamp Lysosomal-associated membrane protein 1, MA Manual acupuncture, MAC-1 Macrophage-1 antigen, MDA Malondialdehyde, NO Nitric oxide, nNos Neuronal nitric oxide synthase, MFB Medial forebrain bundle, MPTP 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, p-p38 MARK Phospho-p38 MAPK, PCNA Proliferating cell nuclear antigen, SD Sprague–Dawley, SOD Superoxide dismutase, TH Tyrosine hydroxylase, TNF-α Tumor necrosis factor alpha, TrkB Tropomyosin receptor kinase B, UBE1 Ubiquitin-like Modifier Activating Enzyme 1, UCH-L1 Ubiquitin C-terminal hydrolase, 5HIAA 5-Hydroxyindoleacetic acid, 5HT 5-hydroxytryptamine, 6-OHDA 6-hydroxydopamine Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 Table Summary of acupuncture for animal PD models (Continued) Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 Page of 10 Fig Sex differences according to the types of animal used as PD model test was mainly used in conjunction with 6-OHDA (8 studies), the pole-climbing test was used in conjunction with MPTP (6 studies), and the swimming test and locomotor counts were each used in conjunction with MPTP (Additional file 3) The rotational behavior test was used in five studies with only males, four studies with a male/ female mix, and one study with animals with undefined sex The studies using the pole-climbing test, the swimming test, and locomotor counts were each conducted with males only Of all studies including behavioral analyses, 72 % (13) of the studies used only male animals, 22 % (4) used a male/female mix, and % (1) used animals with undefined sex In these studies, PD was induced using MPTP in 53 % (9) of the studies and 6-OHDA in 47 % (8) Evaluation of treatment effectiveness The effectiveness of the treatment on PD was evaluated by levels of tyrosine hydroxylase (TH), dopamine (DA), Fig Sex differences according to the method used to induce PD dihydroxyphenyl acetic acid (DOPAC), homovanillic acid (HVA), superoxide dismutase (SOD), glutathione (GSH), and brain-derived neurotrophic factor (BDNF) (Additional file 4) TH was the most frequently used method to determine the effectiveness of the treatment on PD (56 % [32] of the studies) Of the studies using TH, 26 used only males, two used a male/female mix, three used animals with undefined sex, and one used only females Of the studies using DA, ten used only males, five used a male/female mix, and two used animals with undefined sex Of the studies using DOPAC, seven used only males, and two used a male/female mix Of the studies using HVA and GSH, respectively, four of each used only males, and two of each used a male/female mix Of the studies using SOD, four used only males, and two used a male/female mix Of the studies using BDNF, four used only males, one used a male/female mix, and one used only females Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 Page of 10 Fig Sex differences according to the type of acupuncture performed Discussion We analyzed sex differences among previous studies that used animal PD models of acupuncture treatment A total of 810 potentially relevant articles were identified, 57 of which met our inclusion criteria C57/BL6 mice were the most frequently used (42 %) animal PD models Most of the studies evaluating the effectiveness of acupuncture treatment for PD were performed using only male animals (67 %); only one study (2 %) was performed using female animals Many studies have inadvertently excluded females from animal studies of acupuncture treatment for PD Kang et al suggested that acupuncture could be used as a neuroprotective intervention for inhibiting microglial activation and inflammatory events in the MPTP-induced male PD model [52] Yu et al showed that acupuncture treatment displays antioxidative and/or neuroprotective properties in the 6-OHDA lesioned male rat PD models [3] Although a few studies were performed using a male/ female mix, they could not combine and compare the results from male versus female animals Only one report used female animals, in which was a study in which different frequencies of chronic EA stimulation were tested in a partially-lesioned female rat model of PD induced by transection of the MFB This study suggested that long-term high frequency EA is effective in halting the degeneration of dopaminergic neurons in the substantia nigra (SN) Because the studies of male PD models generated using MFB transection are nonexistent, we could not compare the sex differences in this model Taken together, there is currently insufficient evidence from past studies to determine whether there are sex differences in the effectiveness of acupuncture for animal PD models In the future, studies should be performed using a male/female mix to minimize performance bias, and ideally should include a comparison of the sex differences Animal studies have often focused primarily on males For the most part, examination of the differences between males and females has been disregarded in biomedical research, leaving gaps in our knowledge [42] Recently, new drugs have been developed without considering the physiological characteristics of females or sex differences Women have therefore been frequently exposed to dangerous side effects because the experimental studies and clinical trials had mainly used male subjects [70] The lack of female participation in drugdevelopment studies affects males as well as females; when side effects not seen in males during the drug safety checks appear in females, the approval of the drugs is delayed, and male patients waiting for the drugs consequently suffer The NIH requires applicants to report their cell and animal inclusion plans as part of the preclinical experimental design Despite this NIH policy, numerous scientific publications continue to neglect sex-based considerations and analyses in preclinical and clinical research A stronger commitment to reporting sex-specific results will strengthen the evidence base [13] Fortunately, sex differences are increasingly recognized as factors that influence the incidence and disease manifestations of all diseases, including neurodegenerative disorders Some gender differences have been documented for PD [3, 4] Paven et al suggested gender differences in the epidemiology, clinical features, treatment outcomes (medical and surgical/deep brain stimulation), and social impact among all available PD studies [4] Wooten et al performed a meta-analysis of the differences in the incidence of PD between men and women [3] Smith et al summarized evidence that estrogen and selective estrogen receptor modulators are neuroprotective in PD, and reviewed sex differences in basal ganglia function and dopaminergic pathways [71, 72] Consistent with these past studies, if acupuncture research involved both males and females, additional studies of acupuncture for PD would provide a more robust conclusion about sex differences in this treatment Review limitations and future areas of research A number of gaps in the reviewed literature were identified in relation to study quality and findings Study quality could Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 be improved by using female animal models because they reflect the physiological characteristics of both males and females to fully evaluate the effectiveness and safety of the treatment for each sex, which is largely missing in the literature so far Conclusions The results of our review suggest that acupuncture is an effective treatment for animal PD models, but there is insufficient evidence to determine whether sex differences exist in response to this treatment Future studies should examine the effects of acupuncture in animal PD models of both sexes, to reflect the physiological characteristics of females as well as males, and to fully evaluate the effect and safety of this treatment Additional files Additional file 1: Sex differences according to the acupuncture points used (TIF 781 kb) Additional file 2: Sex differences according to behavioral tests used (TIF 776 kb) Additional file 3: Behavioral tests performed categorized by the method used to induce PD (TIF 638 kb) Additional file 4: Sex differences according to the method of evaluation of treatment effectiveness (TIF 842 kb) Abbreviations BDNF: Brain-derived neurotrophic factor; BV: Bee-venom acupuncture; DA: Dopamine; DOPAC: Dihydroxyphenyl acetic acid; EA: Electro-acupuncture; GSH: Glutathione; HVA: Homovanillic acid; MA: Manual acupuncture; MFB: Medial forebrain bundle; MPTP: 1-methyl-4-phenyl-1,2,3,6tetrahydropyridine; SD: Sprague-Dawley; SOD: Superoxide dismutase; TH: Tyrosine hydroxylase; 6-OHDA: 6-hydroxydopamine Acknowledgements We would like to thank Jong-Yeop Kim for his assistance with the collection of data used for this study Funding This work was supported by the Mid-Career Research Program through an NRF grant funded by the Korean government (No 2014R1A2A1A11052795) Availability of data and materials The data sets supporting the conclusions of this article are included within the article Authors’ contributions SHL and SL created the study background and designed the study; SHL performed data acquisition and analysis, and drafted the article; SL conducted the literature review; MvdN, PB and SL revised the article All authors read and approved the final manuscript Competing interests The authors declare that they have no competing interests Consent for publication This information is not relevant Ethics approval and consent to participate Not applicable Page of 10 Author details Department of Applied Korean Medicine, Graduate School, Kyung Hee University, Seoul, Republic of Korea 2Research Group of Pain and Neuroscience, WHO Collaborating Center for Traditional Medicine, East–west Medical Research Institute, Kyung Hee University, Seoul, Republic of Korea Donders Institute for Brain, Cognition and Behaviour, Radboud University, 6525 HR Nijmegen, The Netherlands 4Department of Meridian & Acupoint, College of Korean Medicine, Kyung Hee University, 26 Kyungheedae-ro, Dongdaemun-gu, Seoul 130-70102447, Republic of Korea Received: January 2016 Accepted: 19 October 2016 References Obeso JA, Rodríguez-Oroz MC, Benitez-Temino B, Blesa FJ, Guridi J, Marin C, Rodriguez M Functional organization of the basal ganglia: therapeutic implications for Parkinson's disease Mov Disord 2008;23 Suppl 3:548–59 Samii A, Nutt JG, Ransom BR Parkinson's disease Lancet 2004;363(9423):1783–93 Wooten GF, Currie LJ, Bovbjerg VE, Lee JK, Patrie J Are men at greater risk for Parkinson’s disease than women? J Neurol Neurosurg Psychiatry 2004; 75(4):637–9 Pavon JM, Whitson HE, Okun MS Parkinson's disease in women: a call for improved clinical studies and for comparative effectiveness research Maturitas 2010;65(4):352–8 Wald C, Wu C Biomedical research Of mice and women: the bias in animal models Science 2010;327(5973):1571–2 Haack S, Seeringer A, Thürmann PA, Becker T, Kirchheiner J Sex-specific differences in side effects of psychotropic drugs: genes or gender? Pharmacogenomics 2009;10(9):1511–26 Alvarez-Fischer DC, Noelker F, Vulinović A, Grünewald C, et al Bee venom and its component apamin as neuroprotective agents in a Parkinson disease mouse model Plos One 2013;8(4):e61700 Yan B, Zhigang L, Hu B, et al Effects of electro-acupuncture on Baihui and Taiyang points on caspase- expression and apoptosis of substantia nigra dopaminergic neurons of rats with Parkinson disease Chinese J Tradit Med Sci &Tech 2014;21(5):534–6 Wang YC, Xu YH, Ma J, et al Effects of electric acupuncture on the oxidative stress in the rat of Parkinson’s disease abductioned by rotenone Hubei Univ of TCM 2013;28(8):2417–9 10 Feng J, Sun HM, Wang YY, et al Influences of needling chorea-tremble controlled zone on expressions of dopaminergic neurons and BDNF in mice with Parkinson’s disease J Beijing Univ TCM 2014;37(1):53–7 11 Ding YX, Zhao J, Hou LQ Effects of electroacupuncture on the expressions of neuroal nitric oxide synthase and astrocyte in dentate gyrus of rats with Parkinson's disease Chin acupunct& mox 2013;33(6):533–7 12 Wang SJ, Fang JQ, Ma J Effect of electroacupuncture stimulation of ``Fengfu'' (GV 16) and ``Taichong'' (LR 3) on expression of COX-2 and tyrosine hydroxylase in substantia nigra in rats with Parkinson's disease Acupuncture Research 2013;38(3):198–201 13 Anita H Gender bias in research: how does it affect evidence based medicine? J R Soc Med 2007;100(1):2–3 14 Clayton JA, Collins FS NIH to balance sex in cell and animal studies Nature 2014;509(7500):282–3 15 Raz L, Miller VM Considerations of sex and gender differences in preclinical and clinical trials Handb Exp Pharmacol 2012;214:127–47 16 Singh N, Pillay V, Choonara YE Advances in the treatment of Parkinson’s disease Prog Neurobiol 2007;81(1):29–44 17 Walton-Hadlock J Primary Parkinson's disease: the use of Tuina and acupuncture in accord with an evolving hypothesis of its cause from the perspective of Chinese traditional medicine–part Am J Acupunct 1999; 27(1–2):31–49 18 Choi YG, Yeo S, Hong YM, Lim S Neuroprotective changes of striatal degeneration-related gene expression by acupuncture in an MPTP mouse model of Parkinsonism: microarray analysis Cell Mol Neurobiol 2011;31(3):377–91 19 Yeo S, Choi YG, Hong YM, Lim S Neuroprotective changes of thalamic degeneration-related gene expression by acupuncture in an MPTP mouse model of Parkinsonism: microarray analysis Gene 2013;515(2):329–38 20 Yeo S, Lim S, Choe IH, Choi YG, Chung KC, Jahng GH, Kim SH Acupuncture stimulation on GB34 activates neural responses associated with Parkinson's disease CNS Neurosci Ther 2012;18(9):781–90 Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 Page of 10 21 Choi YG, Park JH, Lim S Acupuncture inhibits ferric iron deposition and ferritin-heavy chain reduction in an MPTP-induced Parkinsonism model Neurosci Lett 2009;450(2):92–6 22 Bai Y, LI ZG, Wang S, et al Study on protective effect of different electroacupuncture on Baihui and Taiyang points on dopaminergic neurons of rats with Parkinson Disease Chin Med Sci Tech 2014a;21(5):536–8 23 Wang SJ, Fang JQ, Ma J, et al Influence of electroacupuncture on p38mitogen activated protein kinase in substantia nigra cells of rats with Parkinson disease model Chin Acupunct Mox 2013b;33(4):329–33 24 Wang YC, He F, Ma J, et al impacts of electroacupuncture on ubiquitinproteasome system in rats with Parkinson’s disease Hubei Univ TCM 2013d; 33(8):725–9 25 Ding YX, Hou LQ, Xiong KR Effect of electroacupuncture on expression of proliferating cell nuclear antigen and glial fibrillary acidic protein in subventricular zone of Parkinson's disease rats Acupunct Res 2012;37(4):286–90 26 Huang Q, Sun Y, Wang L, Zhang Y, et al Acupuncture improve motor function in a mouse model of Parkinson's disease Nucl Tech 2012;35(11):877–80 27 Lu ZY, Zhao H, Wang T Effects of Acupuncture on Behavior and Striatal Apoptosis in Mice with Parkinson Disease Acupunct Res 2012;37(3):186–90 28 Guo CX, Zhang L, Shao SJ, Hao L, et al Oxidative stress effects of electroacupuncture for "Baihui ", "Fengfu", "Yanglingquan " on PD model rat Yunnan Univ TCM 2012;35(5):26–9 29 Yang JL, Chen JS, Yang YF, et al Neuroprotection effects of retained acupuncture in neurotoxin-induced Parkinson's disease mice Brain Behav Immun 2011;25(7):1452–9 30 Kim JI, Yang EJ, Lee MS, et al Bee venom reduces neuroinflammation in the MPTP-induced model of Parkinson's disease Int J Neurosci 2011;121:209–17 31 Du J, Sun ZL, Jia J, Wang X, et al High-frequency electro-acupuncture stimulation modulates intracerebral γ-aminobutyric acid content in rat model of Parkinson’s disease Acta Physiol Sinica 2011;63(4):305–10 32 Wang H, Pan Y, Xue B, et al The Antioxidative Effect of Electro-Acupuncture in a Mouse Model of Parkinson’s Disease PLoS ONE 2011;6(5):e19790 33 Doo AR, Kim ST, Kim SN, et al Neuroprotective effects of bee venom pharmaceutical acupuncture in acute 1-methyl-4-phenyl-1,2,3,6tetrahydropyridine-induced mouse model of Parkinson's disease Neurolog Res 2010;32 Suppl 1:88–91 34 Hong MS, Park HK, Yang JS, et al Gene expression profile of acupuncture treatment in 1-methyl-4-phenyl-1,2, 3,6- tetrahydropyridine-induced Parkinson's disease model Neurol Res 2010;32 Suppl 1:S74–8 35 Jun HJ, Kim YS Dose-dependent Effects of Bee Venom Acupuncture on MPTP-induced Mouse Model of Parkinson's Disease J Korean Acupunct Mox Med Sci 2010;27(5):59–68 36 Kim ST, Moon W, Chae Y, et al The effect of electroaucpuncture for 1methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced proteomic changes in the mouse striatum J Physiol Sci 2010;60:27–34 37 Park W, Kim JK, Kim JI, et al Neuroprotective and Anti-inflammatory Effects of Bee Venom Acupuncture on MPTP-induced Mouse J Korean Acupunct Mox Med Sci 2010;27(3):105–16 38 Sun H, Wu H, Xu H, et al Protective effect of acupuncture in acupoints of Governor Vessel on dopaminergic neurons protection and influence on ultrastructure in mice with Parkinson’s disease Beijing Univ TCM 2010;33(4):257–62 39 Wang YC, Cheng YH, Ma J, et al Effect of electroacupuncture on morphological changes and apoptosis of substantia nigra cells in Parkinson's disease rats Acupunct Res 2010a;35(6):415–21 40 Wang YC, Cheng YH, Ma J, et al Effects of electroacupuncture on the expression of GDNF and Ret in Parkinson’s disease model rats Hubei Univ TCM 2010b;30(9):739–43 41 Wang YY, Sun HM, He X, et al The protection effect of acupuncture of baihui and dazhui points on the dopaminergic neurons in PD mice Prog Anatomic Sci 2010c;16(1):16–20 42 Yu YP, Ju WP, Li ZG, Wang DZ, Wang YC, Xie AM Acupuncture inhibits oxidative stress and rotational behavior in 6-hydroxydopamine lesioned rat Brain Res 2010;1336:58–65 43 Huang PP, Ma J, Wang Y, et al Effect of electroacupuncture on the expression of BDNF and TrKB in mesencephic substantia nigra of the Parkinson 's disease model rats J Hubei Univ Chin Med 2010;12(2):3–5 44 Kim CY, Lee JD, Lee SH Anti-inflammatory Effect of Bee Venom Acupuncture at Sinsu (BL23) in a MPTP Mouse Model of Parkinson Disease J Korean Acupunct Mox Med Sci 2009;26(4):49–58 45 Wang S, Jiang H, Qu L Study on the mechanism of electroacupuncture scalp point penetration therapy in action on apoptosis in the Parkinson's disease rat model Chin Acupunct Mox 2009a;29(4):309–13 46 Wang S, Qi XJ, Han D Effect of electroacupuncture scalp point-throughpoint therapy on the expression of tyrosine hydroxylase and dopamine transporter mRNAs in substantia nigra of Parkinson's disease model rats Chin Acupunct Mox 2009b;29(5):391–4 47 Kim YJ, Kim BS, Park HJ Acupuncture at GB34 modulates laminin expression in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced PD mouse model J Acupunct Acupoint 2008;25(1):155–64 48 Guan T, Sun H, Zhang L, et al The effects of electroacupuncture for iron protein and stained cells in the substantia nigra in Parkinson 's disease model mice Chin J Histochem Cytochem 2008;17(5):427–31 49 Wang S, Qi XJ, Han D Impacts of penetration therapy with head electrical acupuncture on proliferation of neural stem cells in substantia nigra of rat model of Parkinson World J Acu-Mox 2008;18:23–30 50 Jeon S, Kim YJ, Kim ST, et al Proteomic analysis of the neuroprotective mechanisms of acupuncture treatment in a Parkinson's disease mouse model Proteomics 2008;8(22):4822–32 51 Xie XX, Kou ST, Pu ZH, et al Effects of scalp catgut embedding on SOD, NO, MDA in the rat with Parkinson's disease Zhongguo Zhen Jiu 2007;27(10):753–6 52 Kang JM, Park HJ, Choi YG, Choe IH, Park JH, Kim YS, Lim S Acupuncture inhibits microglial activation and inflammatory events in the MPTP-induced mouse model Brain Res 2007;1131(1):211–9 53 Hwang JY, Choi IH, Park JH, et al Acupuncture inhibits microglial activation in the rat model of Parkinson's disease Korean J Meridian Acupoint 2007; 24(1):131–44 54 Luo EL, Zhao FZ, Li GZ, et al Effects of acupuncture on NOS of the medial part of the globus pallidus in rat model of Parkinson's disease J Clinic Acupunct Mox 2007;23(1):54–5 55 Wang Q, Tang CZ, Chen XH, et al Effects of acupuncture on dopaminergic neurons in rats with Parkinson Disease Chin J Basic Med Tradit Chin Med 2007;13(8):621–2 56 Jin Z, Liu TT, Zhou BX Changes of the anti-oxidation capability of rat model of Parkinson disease after acupuncture at subthalamus Chin J Clinic Rehabil 2006a;10(23):188–90 57 Jin Z, Liu TT, Jiang XC, et al Effects of electroacupuncture at subthalamus on dopamine homovanillic acid and dihydroxy-phenyl acetic acid of rats with Parkinson disease Chin J Clinic Rehabil 2006b;10:128–9 58 Ma J, Wang YC, Gan SY Effects of electroacupuncture on behaviors and dopaminergic neurons in the rat of Parkinson's disease Chin Acupunct Mox 2006;26(9):655–7 59 Tang Y, Yu S, Chen J Effect of Electroacupuncture on the Expression of BDNF and BDNF mRNA in Parkinson's Disease Mice Acupunct Res 2006; 31(1):38–42 60 Wang YC, Ma J, Wang H Changes of content of glutamic acid in striatum of rats with Parkinson disease after electroacupuncture stimulation at acupoints Chin J Clinic Rehabil 2006;10:183–5 61 Kim ST, Park HJ, Chae YB, et al Acupuncture at Liver Meridian Protects the Dopaminergic Neuronal Damage in the 1-methyl-4-phenyl-1,2,3,6tetrahydropyridine-induced Parkinson’s Disease Mouse Model Korean J Acupunct 2006;23(4):169–76 62 Kim YK, Lim HH, Song YK, et al Effect of acupuncture on 6hydroxydopamine-induced nigrostratal dopaminergic neuronal cell death in rats Neurosci Lett 2005;384(1-2):133–8 63 Ma J, Zhu SX Effect of electroacupuncture on anti-oxidase in mesencephalic substantia nigra in rats with Parkinson disease Chin J Clin Rehabil 2005;9:120–1 64 Wang YD, Ma J, Wang H Experimental study of the protective effect on dopaminergic neurons in substance nigra of the Parkinsonian rats by the acupuncture therapy of 'Shuanggu Yitong' J Hubei College TCM 2005;7(3):25–6 65 Park HJ, Lim S, Joo WS, et al Acupuncture prevents 6-hydroxydopamineinduced neuronal death in the nigrostriatal dopaminergic system in the rat Parkinson's disease model Exp Neurol 2003;180(1):92–7 66 Liang XB, Liu XY, Li FQ, et al Long-term high-frequency electro-acupuncture stimulation prevents neuronal degeneration and up-regulates BDNF mRNA in the substantia nigra and ventral tegmental area following medial forebrain bundle axotomy Brain Res Mol Brain Res 2002;108:51–9 67 Lin Y, Lin X Comparative study of D2 receptors and dopamine content in striatum before and after electro-acupuncture treatment in rats J Chin Med 2000;113(5):408–11 Lee et al BMC Complementary and Alternative Medicine (2016) 16:430 Page 10 of 10 68 He C, Wang L, Dong H, et al Effects of Acupuncture - Moxibustion on the Contents of Monoamine Transmitters in the Striatum of Rats in Parkinson's Disease Acupunct res 1998;1:44–8 69 Zhu W, Xi G, Ju J Effect of acupuncture and Chinese medicine treatment on brain dopamine level of MPTP-lesioned C57BL mice Acupunct Res 1996;4:46–9 70 Beery AK, Zucker I Sex bias in neuroscience and biomedical research Neurosci Biobehav Rev 2011;35(3):565–72 71 Martin RM, Biswas PN, Freemantle SN, Pearce GL, Mann RD Age and sex distribution of suspected adverse drug reactions to newly marketed drugs in general practice in England: analysis of 48 cohort studies Br J Clin Pharmacol 1998;46(5):505–11 72 Smith KM, Dahodwala N Sex differences in Parkinson's disease and other movement disorders Exp Neurol 2014;259:44–56 Submit your next manuscript to BioMed Central and we will help you at every step: • We accept pre-submission inquiries • Our selector tool helps you to find the most relevant journal • We provide round the clock customer support • Convenient online submission • Thorough peer review • Inclusion in PubMed and all major indexing services • Maximum visibility for your research Submit your manuscript at www.biomedcentral.com/submit ... one article each All of the studies using C57/BL6 animals used only males Of the studies using SD animals, ten used males only, four used a male/female mix, and one used animals with undefined sex. .. Expression of BDNF and BDNF mRNA in Parkinson'' s Disease Mice Acupunct Res 2006; 31(1):38–42 60 Wang YC, Ma J, Wang H Changes of content of glutamic acid in striatum of rats with Parkinson disease. .. 2012;214:127–47 16 Singh N, Pillay V, Choonara YE Advances in the treatment of Parkinson? ? ?s disease Prog Neurobiol 2007;81(1):29–44 17 Walton-Hadlock J Primary Parkinson'' s disease: the use of Tuina and acupuncture